1. Field of the Invention
The present invention relates to a method and an apparatus for heat treating an object, and particularly for heat treating a starting material or an intermediate product for the production of a final product or for the treatment of various products.
2. Related Art
Various heat treatments are used for the production of various products. For example, by heat treatment of an object a number of effects can be obtained such as drying, dehydration, calcination, reaction acceleration, surface modification and so on. In order to improve the efficiency of the heat treatment, an object to be heat treated is passed through a heating chamber in the form of a dome or a tunnel while the object is moved using a conveyer.
An apparatus which carries out such a heat treatment includes a heating zone where temperature of a object is increased to a temperature at which a thermal treatment is started, and a thermally treating zone where such an object of which temperature has been just increased is subjected to predetermined conditions for the thermal treatment (for example, a constant temperature for a predetermined period, or a predetermined temperature change from the increased temperature). There may be no clear border between these two zones. In the present specification, the term "heat treatment (or heat treating)" is intended to include both or either of the temperature increasing treatment in the heating zone and the thermal treatment in the thermally treating zone, which are explained just above. In addition, the apparatus which carries out such a heat treatment usually further includes, at the back of the thermally treating zone, a cooling zone where the object is cooled to a predetermined temperature after the heat treatment. The object passes through these three zones in turn.
With respect to the above heat treatment, there is an energy utilization efficiency problem in that a ratio of an amount of heat energy which is truly used to heat treat the object itself to an amount of heat energy which is supplied to the heat treatment apparatus is small. This means that most of the supplied heat energy is wasted. This problem leads to a high cost for the heat treatment.
In the conventional method for the heat treatment as explained above, the following would be possible reasons for the low heat energy consumption efficiency.
Since an inlet and an outlet of the tunnel shaped heating chamber are always open to the outside, a portion of heat energy supplied to the heating chamber is lost through the inlet and the outlet. An amount of the heat energy lost through the inlet and the outlet is said to be about 30% of the supplied heat energy to the heating apparatus.
In the heating chamber and the conveyer in addition to the object is heated a large amount of heat energy is required to heat up a moving mechanism such as the conveyer. The moving mechanism such as the conveyer is complicated and its heat capacity is large. Thus, a large amount of heat energy is required to heat up the mechanism. The conveyer moves the object from before the heat treatment to after the heat treatment. When the conveyer leaves the heating chamber, heat energy supplied to the conveyer in the heating chamber is taken out to the outside of the heating chamber. Every time the conveyer goes into and out from the heating chamber, a large amount of heat energy is supplied to the conveyer and lost into the outside without being used. An amount of the heat energy lost through the conveyer is said to be about 20% of the heat energy supplied to the heating apparatus.
In addition, an amount of heat which is lost through a wall of the heating chamber to the outside thereof is also large. The amount of the heat energy loss through the wall of the heating chamber is said to be about 45% of the heat energy supplied to the heating apparatus.
Thus, it is said that an amount of heat energy which is substantially used for the heat treatment of the object is only about 5% of the heat energy supplied to the heating apparatus.